Various skin barriers and similar materials are known for these and similar purposes, and it is common for them all that they are adhering to the skin. However, they are not all provided with a watertight film. They all suffer from various drawbacks. Thus, from U.S. Pat. No. 3,339,546 there is known a skin barrier, in the specification called a bandage, adapted to adhere to moist surfaces; especially the oral cavity is aimed at. This known bandage consists of a water-impervious film having secured to one surface thereof an adhesive gum-like bonding composition consisting of a blend of a water soluble or swellable hydrocolloid, e.g. polyvinyl alcohol, powdered pectin, gelatin or carboxymethylcellulose, and a water insoluble viscous gum-like elastic binder, e.g. natural rubber, silicone rubber, polyurethane rubber or notably polyisobutylene. The bandage according to U.S. Pat. No. 3,339,546 is unelastic but to some degree plastic, and the bonding composition rather has the nature of a highly viscous fluid whereas the film is described as polyethylene, which is unelastic. The material is hard and needs substantial force to be deformed, it has a very low elongation at break and does not recover to the original shape after deformation. As it is highly viscous, it only partly follows body movements when placed on movable parts, and if it is used for sealing around ostomies there is a risk of leakage. When using a bandage like this for very curved body parts, e.g. a heel, it is recommended to cut a number of incisions in the edge of a round bandage to enable it to follow the curvatuve of the part of the body; without the incisions the bandage would pucker or go to pieces if one seeks to deform it. The hydrocolloid in the bandage just described ensures that it can adhere to and retain contact with moist, e.g. sweaty surfaces. To improve adhesion and give desired consistency there can optionally be a mineral oil or vaseline present; the viscous gum-like binder gives dry tack and coherence.
From U.S. Pat. No. 3,908,658 there is known a closure and sealing composition for ostomies, also suitable for adhering ostomy-draining pouches to the skin, said composition being water-insoluble and essentially composed of a pressure sensitive adhesion gel body having a uniform surface and internal properties of tack, cohesive strength providing elasticity, flexibility, and compressibility and manual kneadability, said gel consisting essentially of a mixture of mineral oil, styrene-isobutylene copolymer and ethylene-vinyl acetate copolymer. The composition does not typically contain hydrocolloids, but hydrophilic substances such as pregelled starch may be present. This composition has similar drawbacks as the bonding composition according to U.S. Pat. No. 3,339,546, yet has a bigger elongation at break.
To remedy these drawbacks, in British Pat. No. 1,576,522, corresponding to U.S. Pat. No. 4,231,369, there has been proposed a sealing material for ostomy systems having low resistance to quick deformation and rapid recovery to the original shape after deformation, and which consists of a shaped, gel-like blend of a hydrocolloid dispersed in a continuous phase consisting of a physically cross-linked elastomer, viz, a styrene-olefin-styrene block copolymer (or possibly an ethylene-propylene block copolymer) and a hydrocarbon tackifier and optionally also an oil extender and an antioxidant.
This sealing material, which may also be used as skin barrier for other purposes, is splendidly elastic and flexible (whereby is meant bendable out of the plane), it adheres well to the skin and follows its movements and also movements of joints well only the movements are not too big. Because of the hydrocolloid the material absorbs secretions. However, adhesion defects may occur at big movements, e.g. when the material is used as or in bandages at joints. Especially such adhesion defects may occur where the material is used as skin barrier provided with a watertight film on the side turned away from the skin because normal films for the purpose are flexible but unelastic. Adhesion defects may also occur if the material absorbs much moisture, notably if the absorption is irregular. An irregular absorption of moisture may for instance occur at the use as skin barrier over suppurating wounds where the wound itself will yield much liquid, the immediate surroundings less, viz, only sweat. Irregular absorption of moisture may for instance also take place at the use of the material as sealing gasket around stomies, where the parts adjacent the ostomy absorbs liquid from the intestinal discharges and the parts a little more distant only absorb sweat.
By liquid absorption in the known material it causes the material to expand substantially uniformly in all three dimentions (longitudinal and transversal direction, thickness) and this causes a tendency of the material to pucker and let the adhesive contact with the skin go in the areas where the moisture absorption is highest. When using it around ostomies there will occur puckers in the adhesive or sealing material just around the ostomy opening which may give rise to serious skin discomforts because the often very agressive (enzyme-containing) intestinal liquors thereby come into contact with the skin. Also at even supply of moisture the known sealing material just described has a tendency to partly let the skin go and form folds and puckers, especially at its use as bandage on joints because of its three-dimensional expansion combined with the normal unelastic properties of the cover film. The adhesion to the skin is weaker than the forces causing the three-dimensional expansion.
It has now surprisingly been found that the particular drawback of three-dimensional expansion and consequent puckering can be met by the combined measure of reducing the elasticity of the sealing or adhesive material disclosed in U.S. Pat. No. 4,231,369 and bonding that material to an elastic film. It has also been surprisingly found that this reduction of the elasticity of the adhesive material can be achieved by the aid of a plasticizer for the styrene-olefin-styrene block copolymer constituting the elastomer of the said material or at least for the hard styrene blocks thereof. When a material so plasticized or softened absorbs moisture, it will be able to "flow" internally, which means that the forces causing the three-dimensional expansion become weaker because the internal flow may convert the three-dimensional expansion into a largely uni-directional expansion provided that other circumstances favour this; and precisely this is favoured by the bonding of the adhesive material to the elastic film.
In this connection it should be mentioned that U.S. Pat. No. 2,703,573 discloses, i.a., a self-adhering bandage relatively non-adherent to human skin, comprising a strip of fabric coated with an emulsion of styrene latex and a tackifier, said tackifier consisting essentially of an emulsion of polystyrene or a copolymer of styrene and a solvent plasticizer or, e.g., polyethylene glycol di-2-ethyl hexoate; alternatively, the emulsion may be an emulsion of the styrene latex and an emulsified solvent plasticizer, e.g. dioctyl adipate. It is noteworthy that this prior art product is relatively non-adherent to the skin, in contradistinction to the present material, which must be adherent to the skin. As the known material is relatively non-adherent, the problem of losing contact with the skin locally, and puckering, does not exist. Should it exist, it could not be solved by the provisions of the patent; the reason is that the substance plasticized according to the patent is a styrene latex, i.e. a homogeneous material, especially in dried condition when it is no longer a latex, except for variations in the molecular weight (degree of polymerization). The tackifier or plasticizer has the express purpose of retaining self-cohesion at drying, i.e. to enable the emulsified particles of the styrene latex to unite so as to form a coherent mass is relatively non-adherent and free from stickiness.
In connection with the present invention, however, the purpose of the plasticizer is to soften a heterogenous material, the styrene-olefin-styrene block copolymer the blocks of which are mutually incompatible, so that the adhesive material can "flow" internally.
In case there is used a styrene copolymer according to the disclosure of U.S. Pat. No. 2,703,573, it is part of the tackifier and plasticizer emulsion and not a part of the component being plasticized. Apart from this, it is not disclosed what the styrene may be copolymerized with in order to form the copolymer.